Method of production of an alloy

ABSTRACT

A method of production of an alloy wherein powders containing the constituents thereof are intimately mixed, the mixture thus obtained being charged inside a casing, closed with a cover recessed on the face facing the interior of the casing fitted with a bore, the assembly thus obtained being subjected to one compression operation, the bore in the cover being plugged, after which the compressed assembly is subjected to an extrusion operation, the outer layer being subsequently removed by a machining operation. The cover is produced from a metal which at extrusion temperature suffers less deformation than the mixture inside the casing.

United States Patent [72] inventors [21 Appl. No. [22] Filed [45]Patented [73] Assignee C.E.N. Brussels, Belgium [32] Priority Jan. 24,1968 [3 3] Belgium [31] 709,814

[54] METHOD OF PRODUCTION OF AN ALLOY [50] Field of Search 18/12 DM, 14M; 72/272; 29/420, 420.5, 423

[56] References Cited 1 UNITED STATES PATENTS 2,491,897 12/1949 Lorant72/272 2,630,623 3/1953 Chisholm et a1. 29/420 3,040,117 6/1962 Jammet136/175 3,060,560 10/1962 Biehl et a1. 29/4205 3,150,773 9/1964 Richter72/272 X 3,177,573 4/1965 Foerster 29/420 Primary Examiner-John F.Campbell Assistant Examiner-D. C. Reiley Attorney-Stevens, Davis, Miller& Mosher ABSTRACT: A method of production of an alloy wherein powderscontaining the constituentsthereofare intimately mixed, the mixture thusobtained being charged inside a casing, closedwith a cover recessed onthe face facing the interior of the casing fitted with a bore, theassembly thus obtained being subjected to one compression operation, thebore in the cover being plugged, after which the compressed assembly issubjected to an extrusion operation, the outer layer being subsequentlyremoved by a machining operation. The cover is produced from a metalwhich at extrusion temperature suffers less deformation than the mixtureinside the casing.

PATENTEU SEP 7 ml SHEEI 2 0F 2 METHOD OF PRODUCTION OF AN ALLOY Thepresent invention relates to a method of production of an alloy,according to which the powders of the constituents used for making upthe alloy are intimately mixed, the mixture thus obtained is chargedinside a casing, this casing is closed with a cover provided with abore, the assembly thus obtained is subjected to one compressionoperation at least, the bore in the cover is closed with a plug and thecompressed assembly is then subjected to an extrusion operation, afterwhich the outer layer made up by the metal of the casing is removed fromthe extruded product.

A known method of this kind has for its object to produce a ferriticsteel suitable for use as cladding material for fast reactors fuels andis particularly well suited for a carbide (UC or PuC) based fuel. Theuse of such ferritic steel solves the problem set by the increasedbrittleness of the usual cladding materials when irradiated with dosesof nvt magnitude. Such ferritic steel is strengthened by the dispersionof a ceramic oxide in the matrix alloy.

However, this known process was beset with a number of difficulties inconnection with the exhaust of the air when v compressing the powdersbetween the casing and the cover thereof as well as when extruding theassembly comprised of the casing, the contents thereof, i.e. thecompressed powders be noted that the method according to the inventionis notonly an improvement of a known method of production of ferriticsteel, but that it may have other uses, in particular the production ofaustenitic steel and of metal alloys generally, for example nickel basedalloys.

For that purpose a component is used as a cover produced from a metalwhich at the extrusion temperature is subject to less deformation thanthe mixture charged inside the casing and heated to the sametemperature.

For preference a component is used as a cover provided with a recess onthe face facing the interior of the casing.

In a particular form of embodiment of the invention, a component is usedas a cover, the recess thereof is deepest at the said bore.

In a preferred form of embodiment of the invention a component is usedas a cover provided with a recess extending over the whole face facingthe interior of the casing.

An essential condition in order that the known method, to whichreference is made above, shall enable the production of a ferritic steelof excellent quality, wherein the iron, the other metal or metals of thealloy and the ceramic oxide or oxides are homogeneously distributed, isthe intimate mixture of the raw materials and their presence right fromthe start in the shape of a powder with extremely small particles. Anumber of difficulties were encountered when attempting to meet thiscondition. The same difficulties are moreover encountered for eachmethod of production of an alloy carried out in the manner hereinbeforedescribed, in view of the fact that for each production of an alloy ofexcellent quality it is essential that the raw materials available inthe shape of a powder shall be intimately mixed and shall be presentright from the start in the shape of a powder with extremely smallparticles.

According to the invention, the difficulties encountered in thisconnection are met by the fact that the mixed powders are subjected to aball milling inside 'a vibrated container.

In a form of embodiment applied for preference, a motion offset withinits own plane is imparted to the container.

The invention relates not only to the method set forth above, but alsoto the alloy carried out according to such methods.

Other details and features of the invention shall become clear from thedescription of a method of production of an alloy and of the alloy thusobtained according to the invention,

hereinafter given by way of non limiting example and with reference tothe accompanying drawings.

FIG. 1 shows a sectional view of an assembly comprising a casing, thecover thereof and the plug of the latter, used in a method of productionof an alloy according to the invention.

FIGS. 2 to 5 show diagrammatically the general run of the extrusionoperation of a casing, the contents thereof and the cover thereof.

In the different FIGS. the same reference numerals refer to identicalcomponents.

The example hereinafter given refers more particularly to the productionof a ferritic alloy able to be used as a cladding material for the fuelsof fast reactors.

The raw materials used for production of such a steel are in powderform.

There are needed at least one powder containing iron, at least onepowder comprising a ceramic oxide and, as the case may be, at least onemetal powder used for imparting the particular characteristics to thesteel.

The powder containing the iron may be iron powder, e.g. carbonyl-ironpowder of technical purity, i.e. of 99.95 percent purity; this ironpowder is e.g. of 2 to 5 p. fineness.

If the raw material containing the iron is an iron powder the othermetal or metals used to produce with the iron the alloy steel must beadded in powder form. Thus, for example, chromium is added in the shapeof a powder the particles whereof are about 6 to 10 p. in size. Othermetals which may be added in the shape of powders are particularlymolybdenum, tungsten, niobium and vanadium. The powders of such metalsmay be added just as well to an iron powder as to a steel powder, e. g.an A.I.S.I. 410 steel powder.

The ferritic steel produced according to the method having to contain aceramic oxide in the matrix alloy, recourse is also had to at least oneraw material comprising a powder of a ceramic oxide e.g. A1 0 MgO, ZrOTiO or ZrSiO powder. Such powders have to be very fine, for preferencebelow 0.5 11..

Raw materials not available in the shape of a sufficiently fine powderare first subjected to a treatment prior to being able of becoming addedto the mixture, the preparation of which is described hereinafter. Thepreparation of the raw material comprises, e.g. a crushing in a ballmill.

It follows fromthe above that the raw materials for the production offerritic steel comprise at least one iron containing powder, at leastone ceramic oxide powder and, as the case may be, at least one metalpowder. As raw materials may be used for example: 83 percent ironpowder, 13 percent chromium powder, 2 percent molybdenum powder and 2percent titanium oxide powder. 1

The molybdenum may be replaced or supplemented by 1 percent tungsten and0.5 percent niobium. The titanium oxide may be replaced as a whole or inpart by magnesium oxide, zirconium oxide, aluminum oxide or zirconiumsilicate.

The first operation comprises weighing the metal powders, i.e. the iron,chromium, if need be the molybdenum, tungsten and niobium powders.

These metal powders are subsequently intimately mixed, preferably for 20minutes, in a V-mixer. As this device is well known in technology it isnot described in the present patent application.

The ceramic oxide powders, i.e. of magnesium oxide, or titanium oxide,of zirconium oxide or of zirconium silicate are also weighed, and asrequired, subjected to drying.

The ceramic oxide powders are then mixed by hand with the metal powderoriginating from the V-mixer.

The mixture thus obtained is subjected to grinding, for preference in aball mill. Tests have been carried out in this connection using a ballmill having a diameter of 230 mm. rotating at a speed of 60 to r.p.m.This grinding operation is carried out for about 5 hours. In the case ofapplications on an industrial scale, larger sizes would be used and thespeed would be adapted to such sizes.

The mixture originating from the grinder is subjected to a millingoperation which has essentially for its object to crush the ceramicoxides which may agglomerate. Such milling is for preference carried outusing a container having for example the shape of a tray. This tray issubjected to a vibration. Preference to a rotation offset within its ownplane. This tray contains spheres which, in the course of the offsetrotation of the tray move within the latter and crush the oxides. Aspeed of rotation of 200 r.p.m. and an eccentricity of 30 mm. yieldsatisfactory results. This milling is carried out for about 8 hours.

After this operation the raw materials are available in the shape of ahomogeneous mixture. The ceramic oxide powder is available in the shapeof very fine particles in-between the iron particles and those of theother metals.

This mixture of powders is charged in a mild steel case 1. This casingis closed with a cover 2 carried out in a heat resisting steel, forexample 18/8 stainless steel. The mild steel is suitable for the caseand the 18/8 stainless steel is suitable for the cover if the mixture ofpowders is to be used for the production of a ferritic steel. It will bewell understood that the selection of the materials in which the case 1and the cover 2 are carried out depends on the kind of alloy to beproduced. It is essential that at the temperature at which the extrusionis carried out referred to hereinafter, the material of the cover 2shall be less easily deformed than the metal material contained in thecase 1.

At the center of the cover 2 is provided a bore 3 which passes rightthrough the cover 2. On the outside of the cover 2 the bore 3 is widerand enables fitting a plug 4. The outside face 5 of the cover 2 isplane. The inner face 6 of the cover 2, i.e. the face directed towardsthe case is curved, so that the cover 2 is provided with a recess 7directed towards the case. The recess 7 is deepest at the level of thebore 3.

The assembly comprising the casing l, the mixture of powders containedinside such case and the cover 2, the bore 3 of which is not yet pluggedwith the plug 4 is subjected cold to a first compression operation. Bymeans of this operation the cover 2 penetrates partially inside thecasing 1. The pressure applied is such that the powders are subjected toa pressure of 3 l g./mm. magnitude.

By means of this compression the air is expelled from the powders. Theescape of air is favored by the recess 7 which acts as a funnel andleads the air exhausted from the powders towards the bore 3. Because ofthe particular shape of the face 6 of the cover, the powders positionedclose to the cylindrical case wall are compressed before the powderspositioned more in the center of the case shall be compressed. Thus apressure gradient is built up inside the powder mass, such gradientdirecting the air from the cylindrical wall towards the center and fromthere to the funnel provided by the recess 7 and thus to the bore 3. Acover with a plane inner face would tend to apply a higher pressuretowards the center and would thus impede the exhaust of the air.

After the cold compression, the plug 4 is positioned in the top portionof the cover 2. The assembly comprising the case I, the contentsthereof, and the cover 2 is then heated inside a muffle furnace up to atemperature of 700 C. magnitude. The time of heating is about one hourand such heating may be carried out in an inert atmosphere.

The assembly thus heated up is subsequently compressed at suchtemperature of 700 C. in the container of an extrusion press. Initially,the diameter of the casing l is slightly less than the inside diameterof the extrusion press container, but on account of the compression at atemperature of 700 C. the diameter of the case I expands. The pressureat which the said assembly is subjected to the temperature of 700 C. inthe extrusion press container is 100 kg./mm.. By means of this operationthe mixture of powders becomes a compact metallic mass. The air stillescaping from the powders during the heating and the compression at thetemperature of 700 C. is lead through the bore 3 to the plug 4 and isable to accumulate beneath such plug within the free space remainingbetween the face of the plug directed towards the case and the nar'rower portion of the bore.

During the compression at the temperature of 700 C. the cover 2penetrates slightly further inside the case I.

The following operation comprises welding the plug 4 inside the cover 2and welding the latter inside the casing l. The inside of the casing 1wherein is positioned the metallic mass thus provides a hermeticallysealed space.

The case is subsequently subjected to a new machining operation, inorder that it may again easily fit inside the extru sion presscontainer. Simultaneously the head of the case is given a conical shapealong the lines 9 in order that the shape of such head shall be wellfitted for turbulence free extrusion. The assembly comprising thecasing, the contents thereof and the cover thereof is then heated againin salt baths for about 20 minutes to a temperature from 1,100 to l,200C. magnitude. Because of the fact that the plug 4 is welded on the cover2 and that the cover 2 is welded on the case 1, the molten salts cannotenter the inside of the case wherein is positioned the metallic mass.

The assembly heated to the said temperature is subsequently subjected tothe extrusion operation. It is particularly during such operation, thatthe shape of the cover and the fact that at such temperature the coveris less deformable than the material contained inside the case are ofimportance. This is diagrammatically illustrated by the FIGS. 2 to 5,wherein the extrusion equipment is diagrammatically referred to by thereference 10, the material of the casing in the course of transformationbearing the reference 11 and the material of the cover the reference 2.On the left of the line 12 are shown the respective positions prior tothe extrusion. On the right of the same line are shown in the differentFigures the respective positions after the extrusion.

In the four cases shown, the material 1 of the casing is positionedafter the extrusion at the head and on the surface of the extrusionproduct. The FIGS. 2, 3 and 4 refer each time to operations wherein thecover has a face 6 directed towards the inside of the case which isplane. FIG. 5 relates to the case of the cover having the shape shown inFIG. 1.

In the case of the FIG. 2, the resistance to deformation at theextrusion temperature is the same for the metal of the cover 2 and forthe metal 11 inside the case. During the extrusion a deformation of thewall 6 providing the boundary between the metals 11 and 2 will occurhaving the general appearance of line 6. The shape of such line isessentially determined by the friction of the casing against the innerwalls of the container and of the die.

FIG. 3 relates to the case of a metal 11 inside the casing which deformsless easily than the metal of the cover 2. The deformation of theboundary face 6 will then be more marked, in view of the fact that thematerial 2 deforms more easily. As what it is wanted to achieve is analloy of the metal 11, the operation according to FIG. 3 yields anextrusion product which is unusable over a considerable length onaccount of the core provided by the metal of the cover 2.

FIG. 4 relates to the case in which at the extrusion temperature themetal of the cover 2 deforms less easily than the metal 11 inside thecasing. In that particular case, the face 6 is deformed in 6' but in aless marked manner than in the case of FIG. 3 and even than in the caseof FIG. 2. The portion of the extrusion product unusable because of thecore in the material of the cover 2 is therefore shorter.

FIG. 4 relates already to a method according to the invention, but abetter implementation is that according to FIG. 5, which correspondsindeed to that according to FIG. 1. In the case of FIG. 5, the metal ofthe cover 2 deforms, always at the extrusion temperature, less easilythan the metal 11 inside the casing and the face 6 in-between the metalof the cover and the metal 11 of the alloy provided after the extrusion,has the appearance of a plane surface, due to the fact that the cover 2has a recess facing the inside of the case.

The alloy, therefore in the described example the ferritic steel, willbe in the shape of a rod, the cross section of which is determined bythe shape of the die. By means of a known appropriate technique, thealloy may be produced in the shape of a tube. Of the extrusion productonly the portion, the core of which is made up by the alloy, is used andfrom such portion, the outer layer provided by the metal of the casing 1is removed by machining for example.

It has been noted that the output of the method according to theinvention is far superior to the output of the known method referred toin the introduction to the present patent application. The steelachieved according to the invention is highly homogeneous and of veryfine grain. The helium released does not accumulate along the faces ofthe grains and does not therefore give rise to spots of lower resistanceinside the steel.

It will be understood that the invention is in no way limited to theforms of embodiment hereinbefore described and that many changes may beintroduced therein without departing from the scope of the presentpatent application.

Thus for instance the use of the method is in no way limited to theproduction of ferritic steels and this method may be extended to theproduction of austenitic steels and of metal alloys generally, forexample of nickel alloys.

Evidently the appropriate powders have to be used for the production ofthe alloy considered.

The shape of the recess provided inside the cover has likewise to fitthe kind of product to be produced by the extru- SlOl'l.

The dimensions and rates mentioned above relate generally to laboratorytests. Applications on an industrial scale make use of equipment ofappropriate dimensions in order to provide an economically payingproduction and the rates shall correspond to such dimensions.

We claim:

1. A method for the production of an alloy, comprising mixing powders ofthe constituents used for making up the alloy,

charging the resulting mixture inside a metal casing,

closing said casing with a cover provided with a bore'said cover beingmade from a metal which at the temperature of the extrusion is subjectto less deformation than the mixture charged inside the casing,

forcing said cover into said casing in order to compress said mixture,

closing said bore in said cover with a plug, placing said closed casingin an extrusion chamber with the cover remote from the die opening ofthe chamber,

subjecting said closed casing to an extrusion operation in order toproduce an extruded product, the outer layer of which is made up of themetal of the casing, and

removing said outer layer.

2. A method for the production of an alloy, comprising mixing powders ofthe constituents used for making up the alloy,

charging the resulting mixture inside a container having the shape of atray,

subjecting said container to a rotation offset within its own plane,charging said mixture from said container inside a metal casing,

closing said casing with a cover provided with a bore said cover beingmade from a metal which at the temperature of the extrusion is subjectto less deformation than the mixture charged inside the casing,

forcing said cover into said casing in order to compress said mixture,

closing said bore in said cover with a plug,

placing the closed casing in an extrusion chamber with the cover remotefrom the die opening of the chamber,

subjecting said closed casing to an extrusion operation in order toproduce an extruded product the outer layer of which is made up of themetal of the casing, and

removing said outer layer.

2. A method for the production of an alloy, comprising mixing powders ofthe constituents used for making up the alloy, charging the resultingmixture inside a container having the shape of a tray, subjecting saidcontainer to a rotation offset within its own plane, charging saidmixture from said container inside a metal casing, closing said casingwith a cover provided with a bore said cover being made from a metalwhich at the temperature of the extrusion is subject to less deformationthan the mixture charged inside the casing, forcing said cover into saidcasing in order to compress said mixture, closing said bore in saidcover with a plug, placing the closed casing in an extrusion chamberwith the cover remote from the die opening of the chamber, subjectingsaid closed casing to an extrusion operation in order to produce anextruded product the outer layer of which is made up of the metal of thecasing, and removing said outer layer.